Production of cast iron



Patented Nov. 5, 1940 UNITED STATES PATENT OFFICE PRODUCTION OF CASTIRON No Drawing. Original application August 27,

1938, Serial No. 227,182.

Divided and this IP- plication March 26, 1940, Serial No. 326,019

Claims.

This invention relates generally to the production of cast iron and moreparticularly to addition alloys for cast iron, which are added to castiron to improve their engineering and physical properties.

This application is a division of my co-pending application, Serial No.227,182, filed August 27, 1938, for Production of cast iron.

Various alloying elements have been added to cast iron, in order toimprove their strength, hardness, resistance to wear and other physicalproperties. One element which has been used very extensively ischromium. This has the effect of stabilizing the carbides andrestraining carbide decomposition resulting in increased wearresistance, decreased growth at high temperatures, improved strength,hardness and other desirable properties. On the other hand, however, itincreases the tendency of the iron to chill, particularly in thinsections, which for some applications is undesirable. As an example, inthe production of cast iron automotive cylinder blocks, it is oftendesired to have a chromium content of, say, .35 to 50%, in order toimpart to the cast iron the desired physical characteristics ofstrength, hardness and wear resistance along the cylinder bore and valveseats. However, a cylinder block has portions, such as flanges and partsof the water jacket, which are of thin section and, when the requiredamount of chromium alone is used to give the desired characteristics inthe bore of the cylinder block, the flanges and other thin parts arechilled to such an extent that either it is difficult or impossible tomachine them or of the casting.

In order to overcome the chilling tendency of cast iron, whether or notit contains chromium, various other alloying elements have been added.Among these, perhaps the most widely used are nickel and copper.

elements nickel or copper together with chromium is open to certaindisadvantages. In order to counterbalance the chilling effect ofchromium, it is necessary to use about 310% nickel. The ratio of nickelto chromium required for balancing the chilling effect of the chromium50 increases as' the percentage of chromium in the cast iron isincreased. Thus for an iron containing .50% chromium, about 1.75% nickelis needed and for an iron containing .90% chromium, about 3.0% nickel isrequired. The use of these amounts of nickel renders the cost extheycrack during cooling The use of either of these mium, manganese, siliconand iron. The alloy may or may not contain calcium. The use of anaddition alloy containing all three elements chromium, manganese andsilicon. or all four elements chromium, manganese, silicon and calcium,produces results in the treated cast iron which are entirely differentfrom what would be obtained if the elements were used separately or as amere mechanical mixture. Various alloys, for example, ferro-chromium,ferro-manganese and ferrosilicon, have different melting points anddifferent solubilities in cast iron. Thus when these ferro-alloys areadded as a mere mechanical mixture, the chromium, manganese and silicondo not act simultaneously on the bath, but in accordance with theirrespective solubilities and the amounts in which they are present. Ifthe ferro-chromium, ferro-manganese and ferrosilicon are addedsuccessively to the bath, the first added element has an opportunity toreact 25 with the constituents of the bath before the other elements areadded and, therefore, the latter added elements do not have the samebath present on which to reactor with which they may alloy.

The distinction between an addition alloy on the one hand and a meremechanical mixture of alloying elements on the other hand isparticularly pronounced where the alloying elements react with eachother or with elements present 35 in the bath. Cast iron baths alwayscontain oxygen, nitrogen, sulphur and perhaps other impurities to agreater or lesser extent and these impurities vary with difierent baths.Where, therefore, separate additions or a mere mechanical mixture ofalloying elements is used, it can not be predicted beforehand what theeffect of the addition elements in removing or fixing the impuritieswill be or the degree to which each of the addition elements will belost by reacting with the impurities. On the other hand, where myaddition alloy is used and the-amount of impurities in the differentbaths varies, the alloying elements in my alloy are so proportioned thatafter they have performed their deoxidizing function the remainingportions of them are in proportion to produce the desired alloyingeffect.

The addition alloys of my invention produce cast iron having propertieswhich are not at all the same but are vastly superior to the propertieswhich may be imparted to cast iron by the addition thereto of a meremechanical mixture of the various llloying elements or by their separateuse.

My alloy when added to cast iron not only decreases thesection-sensitivity of the cast iron to chill but accomplishes thiswhile retaining or even increasing the physical properties of the castiron, such as tensile strength, hardness and wear resistance. Thechromium increases the tendency of the cast iron to chill and hardensand refines the pearlite matrix of the cast iron. In addition, it is amild deoxidizer. Cast iron always contains certain amounts of oxygen,nitrogen and sulphur, which afl'ect its physical properties.

The manganese in my addition alloy also increases the tendency of thecast iron' to chill, but to a lesser extent than chromium. It stabilizesthe carbides at high temperatures and refines and hardens the pearlitematrix. It is a somewhat stronger deoxidizer than chromium and combineswith sulphur to form manganese sulphide. Since sulphur is a hardener incast iron, its conversion into the form of manganese sulphidecounteracts this tendency to harden the iron.

The silicon is a graphitizer. It strongly retards the tendency of thecast iron to chill. tion, it is a fairly strong deoxidizer and removesoxygen which otherwise would act as a hardner for the cast iron.

The function of the calcium in my addition alloy is to act as a powerfuldeoxidizer and scavenging agent. It is preferred to use calcium or someother scavenging agent, particularly when the cast iron containssubstantial amounts of oxygen, sulphur or nitrogen, but its use,although preferable, is not essential and it may be omitted in someinstances. It will be noted that each of the elements chromium,manganese, silicon and calcium is a deoxidizer and that the efiect ofthese elements ranges from mildly deoxidizing to strongly deoxidizing.The action of my alloy is, therefore, twofold. A certain amount of thealloying elements is used in reacting with the O, N

and S and perhaps other impurities. The remainder has an alloying effecton the cast iron.

The following is a specific example of one type of my addition alloy:

The composition of my addition alloy may be varied within wide ranges,depending upon what efiect it is desired to produce in the cast iron towhich it is ad 'd. The chromium may be between about 1 and 65% but ispreferably between about 25 and 50%. The manganese may be as low asabout 2% or as high as about 50%; but for most uses, it lies betweenabout 5 and 30%. The silicon may be between about 5 and 50% but usuallyis between 10 and 40%. Calcium may or may not be present in the additionalloy but, if present, may be up to about 20% but is preferably not overabout 10% by weight of the alloy. The carbon may be between .10% and 10%but is preferably below about 6%.

In addi- Further examples of my addition alloy are given in Table I.

Addition alloy Test Cr Mn Si Ca G No. percent percent percent percentpercent The column G designates the graphitizing factors of the additionalloys according to the formula as will be more fully explainedhereinafter.

Table II gives the chemical analyses, tensile strengths and Brinellhardness numbers of various cast irons. ignate cast irons made withoutthe use of any addition alloy. Tests 1, 4, 5, 6, 10 and 11 designatecast irons made by adding to base cast irons in the ladle, the additionalloys of Table I, the amount of addition alloy used in each case beingfigured to produce the desired chromium in the finished cast iron.

TABLE II Cast iron containing addition alloys '1. 3. ms. 'r.s Test13.11.11.

31 Mn 1 .0. 01 on 2" 1.2" .315" die. die. dia.

B. H. N.-Brin0ll hardness number.

Cast irons 5 and 6 were made by adding addition alloys 5 and 6respectively to the cast iron designated A. Cast iron 4 was made byadding addition alloy 4 to cast iron B. Cast irons 1 and 10 were made byadding addition alloys 1 and 10 respectively to cast iron C. Cast iron11 was made by adding addition alloy 11 to cast iron D.

It will be noted from Table II that the use of the addition alloysincreases the tensile strength as compared with the untreated cast ironusually 'in the neighborhood of 2,000 to 3,000 pounds per square inch.Also in all cases with the exception of cast iron 11, the Brinellhardness number was increased by the addition of my alloy.

It will be seen that by the use of my alloy chromium may be added tocast iron to impart to it the desirable effects of chromium without,however, increasing the chilling tendency of the iron. In fact, thischilling tendency may be even decreased.

In this table, A, B, C and D des- The effects of the various additionalloys 1, 4, 5, 6, 10 and 11 on chill are shown in the followingTableIII, as is also the chilling effect of chromium alone as obtainedby adding term-chromium to the cast iron.

Turn III Chilling efiect of various addition alloys Chill depth Chilldepth Chill Percent Alloy in mm after m chan chan e G alloy add'n ggg inin chfll 13 6 +7 +116 -32 s 6 +2 +33 -24 c -1 -1c 5 o -1 -1c -4 4 a -2-33 -4 a c -a -50 -4 4. s --1 --50 +8 The data for Table III wereobtained by employing a chill test specimen 4 long x 2" high x A" wide,cast in a core with a thin edge against an iron plate. The depth ofchill was measured in millimeters and'was the amount of penetration ofthe white area from the chilled face.

It will be noted from Table III that the addition of alloys 5, 4, 1, 10and 11 decreased the depth of chili, whereas alloy 6 increased the depthof chill.

In every case, however, the use of -the addition alloys improved thetensile strength and other physical properties of the cast iron. Thus bythe use of my alloys, I may increase the physical properties of castiron and can either increase or decrease the tendency of the iron tochill or can retain the tendency to chill substantially unaltered ascompared with the untreated cast iron.

The fluidity of the molten iron after treatment and its shrinkagecharacteristics also are materially improved.

The percentages of chromium, manganese, silicon, either with or withoutcalcium which should be used in my addition alloy, will depend upon theparticular properties desired in the cast iron. The graphitizing factor(G) of any particular addition alloy may be figured according to thearbitrary formula Applying this formula to the addition alloy given inExample 1,

Referring to Table III, it is seen that the addition alloys have beenarranged in accordance with their increasing (G) values. Alloy 6 havinga (G) value or graphitizing factor of --24 increased the depth of chill33% in the test specimen used. Alloy 5, which had a graphitizing factorof 15, decreased the chill depth 16%. An alloy having a graphitizingfactor of approximately 18 would neither increase nor decrease the chilldepth in the chill test specimen, for chromium contents in the treatediron of approxi-- mately .30 to 50%. Where different amounts of chromiumare introduced, a different graphitizing factor would be required toproduce a balanced alloy, which would neither increase nor decrease thechill when added to a base cast iron.

Although the percentages of chromium, manganese and silicon may bevaried within the ranges given, it is preferred in general commercialpractice that they be selected in such proportions as to give in theaddition alley a ducing element, I may use tungsten, molybdenum,

graphitizing factor (G) between +35 and 35, or preferably between +35and 20. Where either because of section to be cast or composition of theuntreated iron it graphitizes too readily I employ an addition alloyhaving a. high negative 5 graphitizing factor. For example, in castingsof extraordinary sizes beyond the usual foundry practice, I may use anaddition alloy having a graphitizing factor of say -20 to -35. On theother hand, it may be desired to convert an iron which would normally bewhite or mottled as cast into one which is gray as cast. In this case,an addition alloy which has a graphitizing effect may be used. Thus intreating a normal white iron composition, the addition alloy may have agraphitizing factor of, say, +5 to +35. By the use of my addition alloy,the range of size of castings of a given quality which is permissiblewith any given base iron is greatly enlarged.

In using the addition alloy, it is preferably 20 added to the cast ironin the ladle, the amount of addition alloy employed being figured togive the desired chromium content in the cast iron. In general practice,the amount of addition alloy added is sufi'icient to give in the castiron a chromium content of about .10% to 1.0% but this may, of course,be varied considerably.

The invention is not restricted to the use of the addition alloys forproducing gray cast iron but, due to the independent control of chillmade possible by the use of my alloys, the invention is applicable tothe production of chilled cast iron parts, such as car wheels, camshafts and valve tappets, or in the production of articles where it isdesired to have one part chilled and another part machinable.

Addition alloys in accordance with my invention may be made by meltingferro-chromium and silico-manganese in an electric or other furnaceunder a protective slag. Where the alloy is to contain calcium, it maybe added to the melt as calcium silicide or calcium silico-manganese.

The invention has been described with particular reference to additionalloys containing chromium, manganese, silicon and calcium. As abovenoted, however, the calcium may be omitted where such a strongdeoxidizer or scavenging agent is not required. Although I prefer to usechromium as the carbide forming and chill inuranium or vanadium. Insteadof the preferred graphitizing element silicon, I may use nickel, copper,titanium or zirconium. Other strong deoxidizing and scavening elementsmay be employed in place of calcium, such, for example, as strontium,barium, lithium, aluminum or magnesium.

The claims of this divisional application are directed to alloys whichdo not contain efiective amounts of calcium or other equivalentscavenging agents or to a process for using such alloys. The claims ofthe parent application, Serial No. 227,182, are directed to alloys whichcontain effective amounts of calcium or other equivalent scavengingatent or to a process for using such alloys.

The invention is not limited to the preferred examples but may beembodied within the scope of the following claims.

I claim:

1. A preformed alloy for addition to molten cast iron, containing about0.10 to 10% carbon,

balance being substantially all iron except for incidental impurities.

2. A preformed alloy for addition to molten cast iron, containing about0.10 to 10% carbon, about 25 to 50% chromium, about to 30% manganese,and about to 40% silicon, the balance being substantially all ironexcept for incidental impurities.

3. A preformed alloy for addition to molten cast iron, containing about0.10 to 10% carbon, about 10 to 50% chromium, about 2 to 50% manganese,and about 5 to 50% silicon, the

balance being substantially all iron except for incidental impurities,the alloy having a graphitizing factor (G) according to the formulaG=Si(Mn+ Cr) between +35 and 35 4. A preformed alloy for addition tomolten cast iron, containing about 0.10 to 10% carbon, about 10 to 65%chromium, about 2 to 50% manganese, and about 5 to 50% silicon, thebalance being substantially all iron except for incidental impurities,the alloy having a graphitizing factor (G) according to the formulaG=Si(Mn+ Cr) between +16 and -20 5. The process of decreasing thesection-sensitivity of cast iron to chill while maintaining its physicalproperties, which comprises adding to the molten cast iron a preformedalloy containing about 0.10 to 10% carbon, about 10 to 65% chromium,about 2 to 50% manganese and about 5 to 50% silicon, the balance beingsubstantially all iron except for incidental impurities.

6. A preformed alloy for addition to molten cast iron, containing about0.10 to 10% carbon, about 10 to 50% of a carbide forming element of thegroup consisting of chromium, tungsten, n-olybdenum, uranium and.vanadium, about 5 to 50% of a graphitizing element of the groupconsisting of silicon, nickel, copper, titanium and zirconium, and about5 to 50% of manganese, I

the balance being substantially all iron except for incidentalimpurities.

7. The process of making automotive cylinder blocks, which comprisesadding to molten cast iron a preformed alloy containing about 0.10 to10% carbon, about 10 to 65% chromium, about 2 to 50% manganese, andabout 5 to 50% silicon, the balance being substantially all iron exceptfor incidental impurities, the alloy having a graphitiz-' ing factor (G)according to the formula G=Si(Mn+ /2Cr) between and -35 and casting thecylinder block.

8.-A preformed alloy for addition to cast iron containing about 0.10 to10% carbon, about 10 to 65% chromium, about 2 to 50% manganese, and

about 15 to 50% silicon, the balance being sub- G=Si(Mn+ or) between +16and 40 10. An automotive cylinder block of cast iron, in the productionof which a preformed alloy is added to molten cast iron, said alloycontaining about 0.10 to 10% carbon, about 10 to 65% chromium, about 2to manganese and about 5 to 50% silicon, the balance being substantiallyall iron except for incidental impurities.

HENRY T. CHANDLER.

